Free software toolkit

Open-source or just plain free applications to cover 95% of your computing needs. For Mac OS X and Windows users. Disclaimer: These are the applications that I use and prefer, but alternatives exist.

Basics
Browser: Firefox
Office: NeoOffice (Mac), OpenOffice (Win)
Text editing: TextWrangler (Mac), Crimson Editor (Win)
HTML Editing: Nvu
Image Editing: Seashore (Mac), Gimp (Win)
FTP: Cyberduck (Mac), CoreFTP (Win)
Antivirus: ClamXav (Mac), Avast (Win)
Compression: DropCompress (Mac), 7-Zip (Win)

OS-Specific
OS X system optimizer: OnyX
OS X app and file launcher: Quicksilver
Windows PDF creation: PDF Creator
Windows spyware remover: AdAware

Academic and research
Statistics: R
LaTeX engine and frontend: MacTeX (Mac), ProTeXt (Win)